import java.util.Locale;

public class Test {
    public static void main(String[] args) {
        String s = "ABCD";
        String s1 = Solution.toLowerCase(s);
        System.out.println(s1);
    }
}
class Solution {
    public static String toLowerCase(String s) {
        char[] arr = new char[s.length()];
        for(int i = 0; i < s.length();i++) {
            if(s.charAt(i)>='A'&&s.charAt(i)<='Z') {
                arr[i] = (char) (s.charAt(i) + ('a'-'A'));
                continue;
            }
            arr[i] = s.charAt(i);
        }
        String arr1 = new String(arr);
        return arr1;
    }
}